(1) Field of the Invention
The present invention relates to an inert gas debris removal subsystem to carry off particulate contaminants from the radiation-ablated region of a substrate being treated in a photo-ablation system. and specially relates to such a subsystem with multiple chambers having openings which meter a flow of inert gas in a plurality of chambers through openings for controlled partial pressure differentials in such chambers for particulate-flushing gas flow which does not interfere with the ablation beam or cause contaminant build-up.
(2) Description of Related Art
Semiconductor devices and integrated circuits are manufactured using multiple layers of different types of materials. These conductive, semi-conductive and insulation type material are deposited or formed on substrate, semiconductor die, wafer, may be used even simply on their own. The predetermined patterns for packaging electronics, biomaterials, etc are then made by removing material by etching, photolithography, photo-ablation, or other material removal techniques. During photo-ablation, the resonant energy is directly coupled into bond vibrational frequencies. This is done by quickly forcing violent vibrations between atoms so that the bonds break.
A by-product of the laser ablation process is the formation of laser “debris.” The material that is ejected by the laser ablation process consists of gaseous by-products, carbon, and polymer fragments. It is shown that the macroscopic debris does not appear until more than 0.5 μs after the laser pulse is incident on the surface. Since the excimer laser pulse widths are typically less than 50 ns, the ejected debris does not interfere with the incoming light.
The functionality of the imaging is reduced by gaseous and particulate matter and the contamination of the lens elements with the out-gassed particles from the substrate will cause lens distortion and scattering of light from the lens element. Gaseous materials are relatively easier to remove using vacuum, compared with the solid debris material, which is of a greater concern if left unattended. The solids contribute to greater contamination of the surface and may also interfere with incoming light from subsequent pulses. It is therefore advantageous to remove as much as possible of the ejected debris from the ablation area before the next laser pulse begins. Vacuum alone is typically not strong enough to remove the debris from the large volume above the exposed area. A system consisting of forced gas such as nitrogen or helium combined with an exhaust is devised to minimize the effects of the debris and ensure that the exposure site is free of debris prior to the arrival of the next laser pulse.
One common practice for carrying off ablation debris involves the use of an inert gas flow across the laser ablation site. Flushing with an inert gas, or with a semi-inert gas such as nitrogen, is intended to prevent oxidizing reactions, cooling the plume and substrate, and flushing the ablated material away from the ablation site.
Without debris elimination, large carbon fragments can agglomerate or be redeposited into an area under exposure. Most redeposited fragments can be ablated by subsequent pulses. However, under certain conditions (laser fluence, particle dimensions, and mask defects) some of the fragments may be too large for the laser to remove. Under these circumstances, the carbon cluster will prevent ablation of the polymer layer beneath, which results in a carbon-encapsulated “cone” of un-ablated polymer. The task of effectively removing debris becomes even more challenging where vacuum chucks are employed to hold down the substrate material due to the peeling effect of flexible substrates. These issues pose serious reduction in throughput due to reduced efficiencies of the laser in removing material and producing cleaner vias. However, this invention discloses a vacuum debris removal system designed right around the ablation site to work optimally between pulses to effectively remove debris material to produce clean features without affecting the position of a flexible substrate coating.